Formable thermoplastic laminate heated element assembly

ABSTRACT

A semi-rigid heated element assembly and method of manufacturing semi-rigid heated element assemblies is provided. A heated element assembly includes a first thermoplastic sheet, a second thermoplastic sheet, and a resistance heating element laminated between the first and second thermoplastic sheets. The resistance heating element includes a supporting substrate having a first surface thereon and an electrical resistance heating material forming a predetermined circuit path having a pair of terminal end portions. The circuit path continues onto at least one flap portion that is capable of rotating about a first axis of rotation. The reformable continuous element structure may be formed into a final element assembly configuration whereby at least the flap portion is rotated along its axis of rotation to provide resistance heating in at least two planes. Semi-rigid heating elements may be formed into heated containers, heated bags, and other objects with complex heat planes.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This Application is a divisional application of U.S. patentapplication Ser. No. 09/642,215, of Theodore Von Arx, Keith Laken andJohn Schlesselman, filed Aug. 18, 2000, and is related to U.S.application Ser. No. 09/369,779 of Theodore Von Arx, filed Aug. 6, 1999,now U.S. Pat. No. 6,392,208, issued on May 21, 2002, entitled“Electrofusing of thermoplastic heating elements and elements madethereby”; U.S. application Ser. No. 09/416,731, of John Schlesselman andRonald Papenfuss, filed Oct. 13, 1999, now U.S. Pat. No. 6,415,501,issued on Jul. 9, 2002, entitled “Heating element containing sewnresistance material”; U.S. application Ser. No. 09/275,161 of TheodoreVon Arx, James Rutherford and Charles Eckman, filed Mar. 24, 1999, nowU.S. Pat. No. 6,233,398, issued on May 15, 2001, entitled “Heatingelement suitable for preconditioning print media” which is acontinuation in part of U.S. application Ser. No. 08/767,156 filed onDec. 16, 1996, now U.S. Pat. No. 5,930,459, issued on Jul. 27, 1999,which in turn is a continuation in part of U.S. application Ser. No.365,920, filed Dec. 29, 1994, now U.S. Pat. No. 5,586,214, issued onDec. 17, 1996; U.S. application Ser. No. 09/544,873 of Theodore Von Arx,Keith Laken, John Schlesselman, and Ronald Papenfuss, filed Apr. 7,2000, entitled “Molded assembly with heating element captured therein”;U.S. application Ser. No. 09/611,105 of Clifford D. Tweedy, Sarah J.Holthaus, Steven O. Gullerud, and Theodore Von Arx, filed Jul. 6, 2000,entitled “Polymeric heating elements containing laminated, reinforcedstructures and processes for manufacturing same”; and U.S. applicationSer. No. 09/309,429 of James M. Rutherford, filed May 11, 1999, now U.S.Pat. No. 6,263,158, issued on Jul. 17, 2001, entitled “Fibrous supportedpolymer encapsulated electrical component” which are all herebyincorporated by reference.

FIELD OF THE INVENTION

[0002] This invention relates to electrical resistance heating elements,and more particularly to formable thermoplastic laminate heated elementassemblies.

BACKGROUND OF THE INVENTION

[0003] Electric resistance heating elements composed of polymericmaterials are quickly developing as a substitute for conventional metalsheathed heating elements, such as those containing a Ni—Cr coildisposed axially through a U-shaped tubular metal sheath. Good examplesof polymeric heating elements include those disclosed in Eckman, et al.,U.S. Pat. No. 5,586,214 issued Dec. 17, 1996 and Lock, et al., U.S. Pat.No. 5,521,357 issued May 28, 1996.

[0004] Eckman et al. '214 discloses a polymer encapsulated resistanceheating element including a resistance heating member encapsulatedwithin an integral layer of an electrically-insulating,thermally-conductive polymeric material. The disclosed heating elementsare capable of generating at least about 1,000 watts for heating fluidssuch as water and gas.

[0005] Lock, et al. '357 discloses a heater apparatus including aresistive film formed on a substrate. The first and second electrodesare coupled to conductive leads which are electrically connected to theresistive film. The heater also includes an over molded body made of aninsulating material, such as a plastic. Lock, et al. '357 furtherdiscloses that its resistive film may be applied to a substrate, such asa printed circuit board material.

[0006] Laminated heaters are also disclosed in Logan, et al., U.S. Pat.No. 2,710,909, issued Jun. 14, 1955 and Stinger, U.S. Pat. No.3,878,362, issued Apr. 15, 1975. These laminated structures includepartially cured rubber-like substances, backed with layers of glasscloth, such as disclosed in Logan, et al. '909, or the use of adiscontinuous layer of electrically conductive elastomeric materialcontaining conductive carbon adhered to a pair of spaced-apart conductorwires bonded to a durable plastic material, such as Stinger'spolyethylene terephthalate film.

[0007] Other laminated heaters are disclosed in U.S. Pat. No. 2,889,439to Musgrave, issued Jul. 29, 1955, and U.S. Pat. No. 3,268,846 to Morey,issued Aug. 23, 1966. Musgrave discloses a laminated heating panelincluding a resistance wire laminated between two sheets of asbestospaper impregnated with a phenolic resin or plastic. Morey discloses aflexible tape heating element and method of manufacturing the same. Aresistance ribbon is sandwiched between a film of teflon, siliconrubber, or plastic material. There still remains a need, however, for areformable but robust electrical resistance heated element which iseasily adaptable to a variety of end uses and manufacturing processes.There also remains a need for a resistance heating element which iscapable of capturing intricate circuit paths and which is reformable toprovide efficient heating in complex heat planes.

SUMMARY OF THE INVENTION

[0008] The present invention comprises a heated element assembly andmethod of manufacturing heated element assemblies. A heated elementassembly includes a first thermoplastic sheet, a second thermoplasticsheet, and a resistance heating element disposed between the first andsecond thermoplastic sheets. The resistance heating element comprises asupporting substrate having a first surface thereon and an electricalresistance heating material fastened to the supporting substrate, wherethe electrical resistance heating material forms a predetermined circuitpath having a pair of terminal end portions. The resistance heatingelement also includes a first flap portion capable of rotation about afirst axis of rotation where the circuit path continues onto at least aportion of the flap portion. The thermoplastic sheets and resistanceheating element are laminated together to form a reformable continuouselement structure. The continuous element structure is formed into afinal element assembly configuration whereby at least the first flapportion is rotated about the first axis to provide resistance heating inat least two planes.

[0009] The present invention as described above provides severalbenefits. An intricate resistance circuit path of a resistance heatingelement may be secured to a planar supporting substrate and thenlaminated between thermoplastic sheets, whereby the planar resistanceheating element may then be reformed with the laminated structure toprovide heat on a plurality of heat planes. The heated element assemblymay also be secured to a second heated element assembly to form, forexample, a heated containment bag or a heated container. These heatedstructures provide intimate contact between the contents of the heatedstructures and the heat source, thereby providing inherent energyconsumption advantages as well as the ability to intimately locatesecondary devices such as thermistors, sensors, thermocouples, etc . . ., in proximity to the contents being heated or conditions being observedor recorded.

[0010] The heated element assembly also allows for an infinite number ofcircuit path shapes, allowing the circuit path to correspond to thegeneral shape of a desired end product utilizing the heated elementassembly. The heated element assembly may be folded to occupy apredefined space in an end product and to provide heat in more than oneplane, thermoformed into a desired three dimensional heated plane, orstamped or die cut into a predetermined flat shape which may, then, befolded or thermoformed into a desired three dimensional heated shape.The heated element assembly thereby emulates well known sheet metalprocessing or known plastic forming processes and techniques.

[0011] The heated element assembly according to the present inventionmay also be over molded in a molding process whereby the resistanceheating element is energized to soften the thermoplastic sheets and theheated element assembly is over molded with a thermoplastic to form adetailed molded structure. The energizing and overmolding steps may betimed such that the thermoplastic sheets and over molded thermoplasticform a substantially homogenous structure accurately capturing andpositioning the resistance heating element within the structure.Alternatively, the heated element assembly may soften during mold flowwithout additional energizing.

[0012] In another embodiment of the present invention, a sheet of heatedelement assemblies comprises a first thermoplastic sheet, a secondthermoplastic sheet affixed to the first thermoplastic sheet, and asheet of resistance heating elements secured between and to the firstand second thermoplastic sheets. The sheet of resistance heatingelements includes a supporting substrate having a first surface thereonand a plurality of spaced circuit paths, each of the spaced circuitpaths comprising an electrical resistance heating material fastened tothe supporting substrate to form a predetermined circuit path having apair of terminal end portions.

[0013] Each of the circuit paths continue onto a first flap portion of aresistance heating element capable of rotation about a first axis ofrotation. The thermoplastic sheets are laminated together such that thesheet of resistance heating elements is secured between and to the firstand second thermoplastic sheets to form a reformable continuous elementstructure.

[0014] The sheet of heated element assemblies provides several benefits.The sheet may be inexpensively and efficiently produced using massproduction techniques. The sheet may be collected into a roll, allowingthe later separation and use of individual heated element assemblies orgroup of heated element assemblies as described above. The sheet, ratherthan being collected into a roll, may be further processed using varioussecondary fabrication techniques, such as stamping, die cutting, orovermolding.

[0015] The above and other features of the present invention will bebetter understood from the following detailed description of thepreferred embodiments of the invention which is provided in connectionwith the accompanying drawings.

A BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings illustrate preferred embodiments of theinvention, as well as other information pertinent to the disclosure, inwhich:

[0017]FIG. 1 is a front plan view of a resistance heating element,including a resistance wire disposed in a circuit path on a supportingsubstrate and joined to a pair of electrical connectors;

[0018]FIG. 1A is a front plan, enlarged view, of a portion of theresistance heating element of FIG. 1, showing the preferred cross-stitchattachment to the supporting substrate;

[0019]FIG. 2 is a rear plan view of the resistance heating element ofFIG. 1;

[0020]FIG. 3 is a front perspective view of a preferred programmablesewing machine and computer for manufacturing resistance heatingelements;

[0021]FIG. 4 is a top plan view of a heated element assembly including aresistance heating element according to the present invention;

[0022]FIG. 5 is a cross-sectional view of the heated element assembly ofFIG. 4 taken along lines 1-1;

[0023]FIG. 6 is a cross-sectional view of a multilayered heated elementassembly according to the present invention;

[0024]FIG. 7a is a top plan view of a tubular shaped thermoplastic bodyfor providing thermoplastic sheets according to the present invention;

[0025]FIG. 7b is a side elevational view of a tubular shapedthermoplastic body for providing thermoplastic sheets according to thepresent invention;

[0026]FIG. 8 is a front plan view of an exemplary heated containment bagaccording to the present invention;

[0027]FIG. 9 is a cross-sectional view of the containment bag of FIG. 8;

[0028]FIG. 10 is a top plan view of an exemplary heated containment bagaccording to the present invention;

[0029]FIG. 11 is a top plan view of two affixed but partially separatedheated element assemblies according to the present invention shaped toprovide a heated containment bag with a nozzle;

[0030]FIG. 12 is a diagram of an exemplary method of manufacturing asheet of heated element assemblies according to the present invention;

[0031]FIG. 13 is a diagram of a sheet of resistance heating elementsshown in partial according to the present invention;

[0032]FIG. 14 is a top plan view of a resistance heating element whichmay be folded to form a three dimensional heater assembly;

[0033]FIG. 15 is a top plan view of a heating element including theresistance heating element of FIG. 14 where the laminated structure hasbeen cut to form a profile for a heated container; and

[0034]FIG. 16 is a perspective view of a heated container formed fromthe cut heating element of FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention provides thermoplastic laminate heatedelement assemblies including resistance heating elements. As usedherein, the following terms are defined:

[0036] “Laminate” means to unite laminae via bonding them together,usually with heat, pressure and/or adhesive. It normally is used torefer to flat sheets, but also can include rods and tubes. The termrefers to a product made by such bonding;

[0037] “Serpentine Path” means a path which has one or more curves forincreasing the amount of electrical resistance material in a givenvolume of polymeric matrix, for example, for controlling the thermalexpansion of the element;

[0038] “Melting Temperature” means the point at which a fusiblesubstance begins to melt;

[0039] “Melting Temperature Range” means the temperature range overwhich a fusible substance starts to melt and then becomes a liquid orsemi-liquid;

[0040] “Degradation Temperature” means the temperature at which athermoplastic begins to permanently lose its mechanical or physicalproperties because of thermal damage to the polymer's molecular chains;

[0041] “Evacuating” means reducing air or trapped air bubbles by, forexample, vacuum or pressurized inert gas, such as argon, or by bubblingthe gas through a liquid polymer.

[0042] “Fusion Bond” means the bond between two fusible membersintegrally joined, whereby the polymer molecules of one member mix withthe molecules of the other. A Fusion Bond can occur, even in the absenceof any direct or chemical bond between individual polymer chainscontained within said members;

[0043] “Fused” means the physical flowing of a material, such asceramic, glass, metal or polymer, hot or cold, caused by heat, pressureor both;

[0044] “Electrofused” means to cause a portion of a fusible material toflow and fuse by resistance heating;

[0045] “Stress Relief” means reducing internal stresses in a fusiblematerial by raising the temperature of the material or material portionabove its stress relief temperature, but preferably below its HeatDeflection Temperature; and

[0046] “Flap” or “Flap Portion” means a portion of an element which canbe folded without damaging the element structure.

Resistance Heating Element

[0047] With reference to the Figures, and particularly FIGS. 1, 1A and 2thereof, there is shown a first embodiment of a resistance heatingelement 10 having a diameter of about 11 cm. The preferred resistanceheating element 10 may include a regulating device for controllingelectric current. Such a device can include, for example, a thermistor,or a thermocouple, for preventing overheating of the polymeric materialsdisclosed in this invention. The resistance heating elements 10 of thisinvention can take on any number of shapes and sizes, including squares,ovals, irregular circumference shapes, tubes, cup shapes and containershapes. Sizes can range from less than one inch square to 21 in.×26 in.with a single sewing operation, and greater sizes can be available ifmultiple elements are joined together. Greater sizes are also availablewith continuous sewing where a substrate is fed from a roll ofsubstrate.

[0048] As shown in FIG. 1, the resistance heating element 10 includes aresistance wire 12 disposed in a helical pattern or circuit path 18. Theends of the resistance wire 12 are generally riveted, grommeted, brazed,clinched, compression fitted or welded to a pair of electricalconnectors 15 and 16. One circuit path is illustrated in FIGS. 1 and 2.The circuit includes a resistance heating material, which is ideally aresistance heating wire 12 wound into a serpentine path containing about3-200 windings, or, a resistance heating material, such as ribbon, afoil or printed circuit, or powdered conducting or semi-conductingmetals, polymers, graphite, or carbon, or a conductive coating or ink.More preferably the resistance heating wire 12 includes a Ni—Cr alloy,although certain copper, steel, and stainless-steel alloys could besuitable. A positive temperature coefficient wire may also be suitable.The resistance heating wire 12 can be provided in separate parallelpaths, or in separate layers. Whatever material is selected, it shouldbe electrically conductive, and heat resistant.

Substrates

[0049] As used herein, the term “supporting substrate” refers to thebase material on which the resistance material, such as wires, areapplied. The supporting substrate 11 of this invention should be capableof being pierced, penetrated, or surrounded, by a sewing needle forpermitting the sewing operation. Other than this mechanical limitation,the substrates of this invention can take on many shapes and sizes. Flatflexible substrates are preferably used for attaching an electricalresistance wire with a thread. Non-plastic materials, such as glasses,semiconductive materials, and metals, can be employed so long as theyhave a piercable cross-sectional thickness, e.g., less than 10-20 mil,or a high degree of porosity or openings therethrough, such as a grid,scrim, woven or nonwoven fabric, for permitting the sewing needle ofthis invention to form an adequate stitch. The supporting substrate 11of this invention need not necessarily contribute to the mechanicalproperties of the final heating element, but may contain high strengthfibers. Such fibers could contain carbon, glass, aramid fibersmelt-bonded or joined with an adhesive to form a woven or non-woven mat.Alternatively, the supporting substrate 11 of this invention may containordinary, natural, or synthetic fibers, such as cotton, wool, silk,rayon, nylon, polyester, polypropylene, polyethylene, etc. Thesupporting substrate may also comprise a synthetic fiber such as Kevlaror carbon fibers that have good thermal uniformity and strength. Theadvantage of using ordinary textile fibers, is that they are availablein many thicknesses and textures and can provide an infinite variety ofchemistry, porosity and melt-bonding ability. The fibers of thisinvention, whether they be plastic, natural, ceramic or metal, can bewoven, or spun-bonded to produce non-woven textile fabrics.

[0050] Specific examples of supporting substrates 11 useful in thisinvention include non-woven fiberglass mats bonded with an adhesive orsizing material such as model 8440 glass mat available from JohnsManville, Inc. Additional substrates can include polymer impregnatedfabric organic fabric weaves, such as those containing nylon, rayon, orhemp etc., porous mica-filled plate or sheet, and thermoplastic sheetfilm material. In one embodiment, the supporting substrate 11 contains apolymeric resin which is also used in either the first thermoplasticsheet 110 or second thermoplastic sheet 105, or both of a heated elementassembly 100 described below. Such a resin can be provided in woven ornon-woven fibrous form, or in thin sheet material having a thickness of20 mil. or less. Thermoplastic materials can be used for the supportingsubstrate 11 which will melt-bond or liquefy with the thermoplasticsheets 110, 105, so as to blend into a substantially uniform structure.

Sewing Operation

[0051] With reference to FIG. 3, the preferred programmable sewingmachine 20 will now be described. The preferred programmable sewingmachine is one of a number of powerful embroidery design systems thatuse advanced technology to guide an element designer through designcreation, set-up and manufacturing. The preferred programmable sewingmachine 20 is linked with a computer 22, such as a personal computer orserver, adapted to activate the sewing operations. The computer 22preferably contains or has access to, embroidery or CAD software forcreating thread paths, borders, stitch effects, etc.

[0052] The programmable sewing machine 20 includes a series of bobbinsfor loading thread and resistance heating wire or fine resistanceheating ribbon. Desirably, the bobbins are prewound to control tensionsince tension, without excessive slack, in both the top and bottombobbins is very important to the successful capturing of resistanceheating wire on a substrate. The thread used should be of a sizerecommended for the preferred programmable sewing machine. It must haveconsistent thickness since thread breakage is a common mode of failurein using programmable sewing machines. An industrial quality nylon,polyester or rayon thread is highly desirable. Also, a high heatresistant thread may be used, such as a Kevlar thread or Nomex threadknown to be stable up to 500° F. and available from Saunders Thread Co.of Gastonia, N.C.

[0053] The programmable sewing machine of this invention preferably hasup to 6-20 heads and can measure 6 foot in width by 19 feet long. Thesewing range of each head is about 10.6 inches by 26 inches, and withevery other head shut off, the sewing range is about 21 inches by 26inches. A desirable programmable sewing machine is the Tajima Model No.TMLG116-627 W (LT Version) from Tajima, Inc., Japan.

[0054] The preferred method of capturing a resistance heating wire 12onto a supporting substrate 11 in this invention will now be described.First, an operator selects a proper resistive element material, forexample, Ni—Cr wire, in its proper form. Next, a proper supportingsubstrate 11, such as 8440 glass mat, is provided in a form suitable forsewing. The design for the element is preprogrammed into the computer 22prior to initiating operation of the programmable sewing machine 20. Aswith any ordinary sewing machine, the programmable sewing machine 20 ofthis invention contains at least two threads, one thread is directedthrough the top surface of the supporting substrate, and the other isdirected from below. The two threads are intertwined or knotted, ideallysomewhere in the thickness of the supporting substrate 11, so that onecannot view the knot when looking at the stitch and the resultingresistance heating element 10. As the top needle penetrates thesubstrate 11 and picks up a loop of thread mechanically with the aid ofthe mechanical device underneath, it then pulls it upward toward thecenter of the substrate 11 and if the substrate is consistent and thethread tension is consistent, the knots will be relatively hidden. In apreferred embodiment of this invention, the resistance heating wire 12is provided from a bobbin in tension. The preferred programmable sewingmachine 20 of this invention provides a third thread bobbin for theelectrical resistance wire 12 so that the programmable sewing machine 20can lay the resistance wire 12 down just in front of the top needle. Thepreferred operation of this invention provides a zig zag or crossstitch, as shown in FIG. 1A, whereby the top needle criss-crosses backand forth as the supporting substrate 11 is moved, similar to the way anornamental rope is joined to a fabric in an embroidery operation. Asimple looping stitch with a thread 14 is also shown. Sewing by guidingthe top needle over either side of the resistance heating wire 12captures it in a very effective manner and the process is all computercontrolled so that the pattern can be electronically downloaded into thecomputer 22 and automatically sewn onto the substrate of choice.

[0055] The programmable sewing machine 20 can sew an electricalresistance wire 12, 5 mil-0.25 inch in diameter or thickness, onto asupporting substrate 11 at a rate of about 10-500 stitches per minute,saving valuable time and associated cost in making resistance heatingelements.

[0056] The ability to mechanically attach resistive elements, such aswires, films and ribbons, to substrates opens up a multitude of designpossibilities in both shape and material selection. Designers may mixand match substrate materials by selecting their porosity, thickness,density and contoured shape with selected resistance heating materialsranging in cross-section from very small diameters of about 5 mil torectangular and irregular shapes, to thin films. Also, secondary devicessuch as circuits, including microprocessors, fiberoptic fibers oroptoelectronic devices, (LEDs, lasers) microwave devices (poweramplifiers, radar) and antenna, high temperature sensors, power supplydevices (power transmission, motor controls) and memory chips, could beadded for controlling temperature, visual inspection of environments,communications, and recording temperature cycles, for example. Theoverall thickness of the resistance heating element is merely limited bythe vertical maximum position of the needle end, less the wire feed,which is presently about 0.5 inches, but may be designed in the futureto be as great as 1 inch or more. Resistive element width is not nearlyso limited, since the transverse motion of the needle can range up to afoot or more.

[0057] The use of known embroidery machinery in the fabrication ofresistance heating elements allows for a wide variety of raw materialsand substrates to be combined with various resistance heating materials.The above construction techniques and sewing operation also provide theability to manufacture multi-layered substrates, including embeddedmetallic and thermally conductive layers with resistance wires wrappedin an electrically insulating coating, so as to avoid shorting ofelectric current. This permits the application of a resistance heatingwire to both sides of the thermally conductive metallic layer, such asaluminum foil, for more homogeneously distributing resistance heat.

Thermoplastic Laminate Heated Element Assembly and Heated ContainerConstruction

[0058]FIG. 4 is a top plan view of a heated element assembly 100according to the present invention. The heated element assembly 100includes a first thermoplastic sheet 110 and a second thermoplasticsheet 105 laminated to the first thermoplastic sheet 110. Forillustrative purposes, second thermoplastic sheets 105 is shownpartially removed from first thermoplastic sheet 110. A resistanceheating element 10, described above, is laminated between and to thefirst and second thermoplastic sheets 110, 105 such that thethermoplastic sheets 110, 105 substantially encompass the circuit path18, which includes resistance wire 12.

[0059] The supporting substrate of the resistance heating element 10 ispreferably not thicker than 0.05 inch, and more preferably 0.025 inch.The supporting substrate should be flexible, either under ambientconditions or under heat or mechanical stress, or both. A thinsemi-rigid heated element assembly 100 allows for closer proximity ofthe resistance heating wire 12 to an object to be heated when the heatedelement assembly is formed into a final element assembly, such as acombination containment bag and heater. Thin element assembliesaccording to the present invention provide the flexibility to choosematerials with lower RTI (Relative Thermal Index) ratings because lessheat needs to be generated by the resistance heating element 10 toprovide heat to the outer surfaces of the heating element assembly 100.

[0060] The thermoplastic sheets 110, 105 are laminated to each other tosecure resistance heating element 10 and to form a reformable continuouselement structure. The thermoplastic sheets 110, 105 may be heated andcompressed under sufficient pressure to effectively fuse thethermoplastic sheets together. A portion of this heat may come fromenergizing the resistance heating element 10. Alternatively, aresistance heating element 10 may be placed within a bag-shapedthermoplastic body (not shown) where the top layer of the bag may beconsidered a thermoplastic sheet and the bottom layer of the bag may beconsidered a thermoplastic sheet (e.g., two thermoplastic sheets securedalong mating edges, but providing an opening for insertion of theresistance heating element 10). Air from within the bag may beevacuated, e.g., by pulling a vacuum, thereby collapsing the bag aroundthe resistance heating element 10, and then heat and/or pressure may beapplied to the collapsed structure to create a single heated elementassembly 100. Also, heated element assembly 100 may be formed byextruding a tubular shaped thermoplastic body 107 (FIGS. 7a and 7 b),disposing a resistance heating element 10 within the thermoplastic body107, and heating and compressing the body 107, particularly along edges108, to secure the heating element 10 within the thermoplastic body.Regardless of the initial form the thermoplastic sheets take,thermoplastic sheets are preferably laminated such that a flexiblecontinuous element structure is created, including a resistance heatingelement 10 and preferably with little air trapped between thethermoplastic sheets.

[0061] Preferred thermoplastic materials include, for example:fluorocarbons, polypropylene, polycarbonate, polyetherimide, polyethersulphone, polyaryl-sulphones, polyimides, and polyetheretherkeytones,polyphenylene sulfides, polyether sulphones, and mixtures andco-polymers of these thermoplastics.

[0062] It is further understood that, although thermoplastic plasticsare most desirable for fusible layers because they are generallyheat-flowable, some thermoplastics, notably polytetraflouroethylene(PTFE) and ultra high-molecular-weight polyethylene (UHMWPE) do not flowunder heat alone. Also, many thermoplastics are capable of flowingwithout heat, under mechanical pressure only.

[0063] Good results were found when forming a heated element assemblyunder the conditions indicated in TABLE 1 as follows: TABLE THICKNESS OFSHEET PRESSURE TIME TEMP. MATERIAL (mil) (PSI) (minutes) (° F.)Polypropolyne 9 22 10 350 Polycarbonate 9 22 10 380 Polysulfune 19 22 15420 Polyetherimide 9 44 10 430 Polyethersulfone 9 44 10 460

[0064] where no vacuum was pulled, “thickness” is the thickness of thethermoplastic sheets in mils (1 mil=0.025 mm=0.001 inch), “pressure”represents the amount of pressure applied to the assembly duringlamination, “temperature” is the temperature applied during lamination,and “time” is the length of time that the pressure and heat wereapplied.

[0065] The first and second thermoplastic sheets 110, 105 and resistanceheating element 10 of the heated element assembly 100 may also belaminated to each other using an adhesive. In one embodiment of thepresent invention, an ultraviolet curable adhesive may be disposedbetween the resistance heating element 10 and the first thermoplasticsheet 110 and between the resistance heating element 10 and the secondthermoplastic sheet 105, as well as between areas of the thermoplasticsheets 110, 105 which are aligned to be in direct contact. Anultraviolet curable adhesive may be used that is activated byultraviolet light and then begins to gradually cure. In this embodimentof the present invention, the adhesive may be activated by exposing itto ultraviolet light before providing the second of the thermoplasticsheets 110, 105. The thermoplastic sheets 110, 105 may then becompressed to substantially remove any air from between the sheets 110,105 and to secure resistance heating element 10 between thethermoplastic sheets 110, 105.

[0066]FIG. 6 illustrates that a heated element assembly 100 a accordingto the present invention may include a plurality of heated layers. Asecond resistance heating element 10 a may be laminated between and tothermoplastic sheet 110 and a third thermoplastic sheet 115.

[0067] The thicknesses of thermoplastic sheets 110, 105 and thethickness of supporting substrate 11 and resistance heating material 12are preferably selected to form a reformable continuous elementstructure that maintains its integrity when the element is formed into afinal element structure. The heated element assembly 100 according tothe present invention, then, is a semi-rigid structure in that it may bereformed, such as by simply folding or folding under heat, pressure, ora combination thereof as required by the chosen thermoplastics, into adesired shape without sacrificing the integrity of the structure.

[0068]FIG. 8 is a side elevational view of an exemplary combinationheated containment bag and heater 150 with flexible walls according tothe present invention. The containment bag 150 includes at least a firstand second heated element assemblies 100. FIG. 9 is a cross-sectionalview of the containment bag 150, and FIG. 10 is a top plan view of thecontainment bag 150. Two or more heated element assemblies 100 may bealigned along mating edges 120, and the edges 120 may be fused orotherwise sealed to form a heated containment bag 150 having an enclosedarea, designated generally as area 123, for holding contents.Alternatively, a single heated element assembly 100 may be folded into abag or container shape and its mating edges may be fused to form aheated containment bag. The assembly 100 may also be heated tofacilitate folding into the containment bag shape and enable theassembly to maintain the containment bag shape after cooling. Thecontainment bag 150 preferably has flexible sidewalls formed from heatedelement assemblies 100 which are capable of substantially conforming tothe contents contained in area 123, thereby efficiently heating thecontents of the containment bag 150.

[0069] The heated containment bag 150 preferably includes a dispensingmeans 125, i.e., a nozzle or spout, that allows the contents of theheated containment bag 150 to be inputted and expelled. The nozzle 125may be included as a separate structure captured and sealed along anedge 120 or other area on a containment bag 150. Alternatively, eachheated element assembly 100 a may be shaped to include a portion of thenozzle, as shown in FIG. 11. A nozzle 125 a may then be formed when theheated element assemblies 100 a are mated and fused along edges 120 a.The dispensing region 135 can either be fused along with edges 120 a andlater punctured or otherwise be left open or be plugged. Thisalternative of forming a nozzle from appropriately shaped heated elementassemblies 100 a provides the added benefit of allowing the circuit path18 of the resistance heating element 10 of at least one of the heatedelement assemblies 100 a to continue into the nozzle shaped area inorder to provide heat to the nozzle area, thereby preventing blockagesfrom forming and providing a uniformly heated container. This embodimentmay be used, for example, for a containment bag as used in a hot cheesedispenser where the dispenser is not used for lengthy, and irregular,periods of time.

[0070] Heated containers 150 according to the present invention provideseveral advantages over non-rigid and rigid containers which do and notinclude a heat source according to the present invention. The heatsource, i.e., the resistance heating element 10, intimately surroundsthe contents of the container 150, which may be, for example, bloodplasma, food product, or other contents, whether they be gaseous,liquid, solid, or semi-solid. The product's packaging is capable ofeffectively doubling as its heat source, thereby removing layers ofmaterial or air space between the contents and its heat source as wellas eliminating the need for an external heat source. Also, secondarydevices as described above, such as temperature gauges, may be disposedmore intimately with the contents or conditions that are beingmonitored.

[0071] A heated element assembly 100 may also be positioned in a moldand over molded to form a selected molded heated structure. A heatedelement assembly 100 may optionally be thermoformed to conform to atleast a part of the mold structure and to preferentially align theresistance heating element within the mold. Once the heated elementassembly is positioned within a mold, the resistance heating element 10of the heated element assembly 100 may be energized to soften thethermoplastic sheets, and the heated element assembly may be over moldedwith a thermoplastic. The energizing and overmolding may be timed suchthat the thermoplastic sheets and over molded thermoplastic form asubstantially homogenous structure when solidified. Alternatively, thethermoplastic sheets may be allowed to soften as a result of mold flowalone. The thermoplastic materials of the sheets and over moldedthermoplastic are preferably matched to further facilitate the creationof a homogenous structure. The supporting substrate 11 may also beselected to be a thermoplastic to better promote the formation of ahomogenous structure. The energizing may be timed to soften thethermoplastic sheets before, after, or during the overmolding process,depending upon the standard molding parameters, such as the flowcharacteristic of the selected thermoplastics, the injection moldingfill time, the fill velocity, and mold cycle. The assembly is alsoamenable to other molding processes, such as injection molding,compression molding, thermoforming, and injection-compression molding.

[0072]FIGS. 14, 15, and 16 illustrate an exemplary heated elementassembly which may be formed into a heated container final elementassembly. FIG. 14 is a top plan view of an exemplary resistance heatingelement 400. The resistance heating element 400 includes a supportingsubstrate 405 shaped in the profile of a flattened container. Theprofile may either be initially shaped in this profile shape or cut tothe profile shape from a larger supporting substrate. Resistance heatingmaterial is affixed to the supporting substrate 405 and is preferablyresistance wire 410 sown to supporting substrate 405.

[0073] The resistance heating element 400 shown in FIG. 14 includes aplurality of flap portions 420 capable of rotation about a first axis ofrotation indicated generally at joints 425. The circuit path 415 formedby resistance wire 410 continues onto flap portions 420 and terminatesat terminal end portions 412.

[0074]FIG. 15 is a top plan view of a heating element assembly 500. Theresistance heating element 400 is laminated between two thermoplasticsheets, only the top sheet 510 of which is shown, to form a reformablecontinuous element structure. A portion of the thermoplastic sheet 510is shown removed in order to show the resistance heating element 400.

[0075] The dashed lines 530 indicate portions of the laminated structurethat may be removed, such as by stamping or die cutting, from thelaminated structure to leave a foldable profile which may be formed intothe a non-planar container 600 shown in FIG. 16. The remaining dashedlines of FIG. 15 indicate fold lines. The heating element assembly 500preferably includes joining tabs 540 which may be used to help form theheated container 600 final element assembly shown in FIG. 16 anddescribed below.

[0076] Heated container 600 may be formed by folding the heating element500 along the dashed lines of FIG. 15 and in the direction of the arrowsshown in FIG. 16. The flaps 420 of the resistance heating element 400are laminated between thermoplastic layers and are folded into thecontainer shape shown in FIG. 16. The folding step may includerethermalizing the thermoplastic structure while folding in order tothermoform the structure into the desired heat planes. The thermoplasticjoining tabs 540 may then be folded to mate with an adjacent surface ofthe continuous element structure. The joining tabs 540 are preferablyheated to fuse them to the adjacent surfaces. The container 600 may evenbe made fluid tight if each mating edge is fused or if the joining tabs540 cover all seams between adjacent surfaces.

[0077] It should be apparent that the container 600 provides heat onfive different interior planes may, but is formed from an easilymanufactured planar heating element 500. It should further be apparentthat the present invention is not limited in any way to the containerstructure 600 or heating element 500 described above. Rather, the abovedescribe method of manufacturing and heating element structure may beused to forms cups, enclosed containers, boxes, or any other structurewhich may be formed from a planar profile.

[0078] A sheet of heating elements and a method of manufacturing thesame is described hereafter. In another exemplary embodiment of thepresent invention, a sheet of heated element assemblies 225 is provided,as shown in FIG. 12. The sheet of heated element assemblies 225 includesa first and second affixed thermoplastic sheets, as described above, anda sheet of resistance heating elements 200 (FIG. 13) secured between andto the first and second thermoplastic sheets. Essentially, the sheet ofresistance heating elements 200 comprises a plurality of connectedresistance heating elements 10. The sheet of resistance heating elements200 comprises a supporting substrate 205 and a plurality of spacedcircuit paths 207, each of the spaced circuit paths comprising anelectrical resistance heating material fastened to the supportingsubstrate 205 to form a predetermined circuit path having a pair ofterminal end portions 209, 210. The shape of the circuit path 207 ismerely illustrative of a circuit path shape, and any circuit path shapemay be chosen to support the particular end use for a heated elementassembly included in the sheet of heated element assemblies 225. Thedashed lines of FIG. 13 indicate where an individual resistance heatingelement may be removed from the sheets of resistance heating elements225.

[0079] A sheet 225 of heated element assemblies may be manufacturedusing conventional mass production and continuous flow techniques, suchas are described in U.S. Pat. No. 5,184,969 to Sharpless et al., theentirety of which is incorporated herein by reference. For example, asillustrated in FIG. 12, first and second thermoplastic sheets 211, 212may be provided from a source, such as rolls 214, 216 of thermoplasticsheets, or extruded using known extrusion techniques as a part of themanufacturing process. One manufacturer of such thermoplastic sheetextruders is Killion Extruders inc. of Cedar Grove, N.J. Likewise, asheet of resistance heating elements 200 may be provided from a source,such as roll 218. Sheet 200 may be manufactured as described above inthe “Sewing Operation” section. The sheets 200, 211, 212 may be made toconverge, such as by rollers 224, between a heat source, such as radiantheating panels 220, to soften the thermoplastic sheets 211, 212. Aseries of rollers 222 compresses the three sheets 200, 211, 212 into asheet of heated element assemblies 225, thereby also removing air frombetween the sheets 200, 211, 212. The rollers 222 may also provide heatto help fuse the sheets 200, 211, 212 and/or may be used to cool freshlylaminated sheets 200, 211, 212 to help solidify the heated sheets intothe sheet of heated element assemblies 225 after compression.

[0080] It should be apparent that a sheet of a plurality ofmultiple-layered heating element assemblies, such as a sheet including aplurality of heating element assemblies 100 a of FIG. 6, may also bemanufactured simply by including a third thermoplastic sheet and asecond sheet of resistance heating elements to the process-describedabove.

[0081] A sheet of heated element assemblies may also be manufacturedusing blown film processes and techniques. Blown film extruders areavailable from the Windmoeller & Hoelscher Corporation of Lincoln, R.I.A sheet of resistance heating elements 200 may be introduced within ablown cylindrical extrusion mass before the mass is collected into athin film. In this manner, a sheet of resistance heating elements iseffectively laminated between a first and second thermoplastic sheets,i.e., between the two halves of the cylindrical extrusion mass.

[0082] Regardless of the specific manufacturing technique, the sheet ofheated element assemblies 225 may be collected into a roll 230. The roll230 may then be used by an original equipment manufacture (OEM) for anydesired manufacturing purpose. For example, the OEM may separate or cutindividual heated element assemblies from the roll and include theheated element assembly in a desired product, e.g, a container or moldedproduct. An individually manufactured heated element assembly asmentioned above or a heated element assembly removed from a sheet ofheated element assemblies 225 is amenable to secondary manufacturingtechniques, such as die cutting, stamping, or thermoforming to a desiredshape or combination thereof as described above. Each heated elementassembly may be cut or stamped into a preselected shape for use in aparticular end product even while still a part of sheet 225 and thencollected into a roll 230. The circuit path of the resistance heatingelement of the heated element assembly may be appropriately shaped toconform to the desired shape of a selected product and heat planes inwhich the heated element assembly is to be included or formed.

[0083] The formable semi-rigid feature of the heated element assembliesof the present invention provides a designer the opportunity to includethe assembly in complex heat planes. The assembly may be cut to adesired formable shape, and the circuit path is preferably designed tosubstantially conform to this shape or the desired heat planes. Theassembly may then be rethermalized and folded to conform to the heatplanes designed for the assembly to occupy.

[0084] A preferred thermoplastic sheet may range from approximately0.004 inch to 0.100 inch. Thus, the thickness of the thermoplasticsheets of a heated element assembly may be chosen to effectively biasheat generated by a resistance heating element in a selected direction.For example, referring to the heated containment bag 150 discussedabove, the outer thermoplastic sheets of the heated element assemblies100 may be chosen to be thicker than the interior thermoplastic sheets(those sheets contacting any contents of the containment bag 150) of theheated element assemblies 100. In doing so, heat generated by theheating element assemblies 100 may be effectively biased toward thecontents of the containment bag 150 and away from the container'ssurroundings. The supporting substrate itself may provide an insulationbarrier when the circuit path is oriented towards, for example, contentsto be heated and the supporting substrate is oriented toward an outer orgripping surface.

[0085] Similarly, one or both of the thermoplastic sheets of a heatedelement assembly 100 or heated element assembly 500 may be coated with athermally conductive coating that promotes a uniform heat plane on theheated element assembly. An example of such a coating may be found onanti-static bags or Electrostatic Interference (ESI) resistive bags usedto package and protect semiconductor chips. Also, thermally conductive,but preferably not electrically conductive, additive may be added to thethermoplastic sheets to promote heat distribution. Examples of suchadditive may be ceramic powders, such as, for example, Al₂O₃, MgO, ZrO₂,boron nitride, silicon nitride, Y₂O₃, SiC, SiO₂, TiO₂, etc . . . Athermally conductive layer and/or additive is useful because aresistance wire typically does not cover all of the surface area of aresistance heating element 10.

[0086] As described above, the heated element assembly of the presentinvention lends itself to many automated and secondary manufacturingtechniques, such as stamping, die cutting, and overmolding, to name afew. Designers can easily choose thermoplastics and other materials fortheir designs that meet required RTI (relative thermal index)requirements for specific applications by following standard designtechniques and parameters set by materials manufacturers Also, heatedcontainers such as described above allow the food industry toefficiently and effectively reheat prepared foods, as is often requiredof businesses that operate large or small food service venues or thatpurchase from distributors of prepared foods. Also, among the manyadvantages of the present invention is the ability to intimately locatea secondary device captured between the thermoplastic sheets, such as amemory device or other data collector within close proximity to a foodproduct, thereby allowing more accurate data collection. This data, asan example, may be used to prove that a food was prepared at atemperature and for a time period sufficient to kill the E. colibacteria.

[0087] Although various embodiments have been illustrated, this is forthe purpose of describing, but not limiting the invention. For example,a heated container could be formed from more than two heated elementassemblies. The heated containers of the present invention, also, are byno means limited to food products, but may have utility in manyindustries, such as the medical industry. Further, the assembly linedescribed above is merely illustrative of one means of forming a sheetof heated element assemblies. More, the supporting substrate shapes andcircuit paths described above and shown in the drawings are merelyillustrative of possible circuit paths, and one of ordinary skill shouldappreciate that these shapes and circuit patterns may be designed inother manners to accommodate the great flexibility in uses and number ofuses for the heated element assembly of the present invention.Therefore, various modifications which will become apparent to oneskilled in the art, are within the scope of this invention described inthe attached claims.

What is claimed is:
 1. A heated element assembly, comprising: (a) a first thermoplastic sheet; (b) a second thermoplastic; and (c) a resistance heating element secured between and to said first and second thermoplastic sheets, said resistance heating element comprising: (i) a supporting substrate having a first surface thereon; (ii) an electrical resistance heating material fastened to said supporting substrate, said electrical resistance heating material forming a predetermined circuit path having a pair of terminal end portions; and (iii) a first flap portion capable of rotation about a first axis of rotation, said circuit path continuing onto at least a portion of said flap portion wherein said thermoplastic sheets and resistance heating element are laminated together to form a reformable continuous element structure, said reformable continuous element structure formed into a final element assembly configuration whereby at least said first flap portion is rotated about said first axis to provide resistance heating in at least two planes.
 2. The heated element assembly of claim 1, wherein said thermoplastic sheets are affixed with an adhesive.
 3. The heated element assembly of claim 1, wherein said reformable continuous element structure is thermoformed into said final element assembly configuration.
 4. The heated element assembly of claim 1, wherein said reformable continuous element structure is cut into a foldable profile, said foldable profile including at least one joining tab, said joining tab mated to an adjacent surface of said reformable continuous element structure when said reformable continuous element structure is formed into said final element assembly configuration.
 5. The heated element assembly of claim 1, wherein said electrical resistance heating material is glued, sewn, fused, or a combination thereof to said supporting substrate.
 6. The heated element assembly of claim 5, wherein said electrical resistance heating material is sewn to said supporting substrate with a thread.
 7. The heated element assembly of claim 1, wherein said supporting substrate comprises a woven or non-woven fibrous layer.
 8. The heated element assembly of claim 1, wherein said supporting substrate is a thermoplastic sheet.
 9. The heated element assembly of claim 1, wherein said supporting substrate includes thermally conductive additives.
 10. The heated element assembly of claim 1, wherein at least one of said thermoplastic sheets includes a thermally conductive coating.
 11. The heated element assembly of claim 1, further comprising a secondary device secured between said first and second thermoplastic sheets.
 12. The heated element assembly of claim 1, wherein one of said thermoplastic sheets is thicker than the other thermoplastic sheet.
 13. The heated element assembly of claim 1, wherein said heated element assembly is over molded with a thermoplastic such that said over molded thermoplastic and thermoplastic sheets form a substantially homogenous structure.
 14. The heated element assembly of claim 1, wherein said supporting substrate is shaped as a foldable profile of a container, said foldable profile including said first flap portion.
 15. A sheet of heated element assemblies, comprising: (a) a first thermoplastic sheet; (b) a second thermoplastic sheet; and (c) a sheet of resistance heating elements secured between and to said first and second thermoplastic sheets, said sheet of resistance heating elements comprising: (i) a supporting substrate having a first surface thereon; and (ii) a plurality of spaced circuit paths, each of said spaced circuit paths comprising an electrical resistance heating material fastened to said supporting substrate to form a predetermined circuit path, said circuit path having a pair of terminal end portions, each of said circuit paths continuing onto a first flap portion of a resistance heating element capable of rotation about a first axis of rotation; and wherein said first and second thermoplastic sheets and resistance heating elements are laminated such that said sheet of resistance heating elements is secured between and to said first and second thermoplastic sheets to form a continuous element structure.
 16. The sheet of heated element assemblies of claim 15, further comprising an adhesive affixing said first and second thermoplastic sheets.
 17. The sheet of heated element assemblies of claim 15, wherein said electrical resistance heating material is glued, sewn, fused, or a combination thereof to said supporting substrate.
 18. The sheet of heated element assemblies of claim 17, wherein said electrical resistance heating material is sewn to said supporting substrate with a thread.
 19. The sheet of heated element assemblies of claim 15, wherein said supporting substrate comprises a woven or non-woven fibrous layer.
 20. The sheet of heated element assemblies of claim 15, wherein said supporting substrate is an extruded thermoplastic sheet.
 21. The sheet of heated element assemblies of claim 15, further comprising a plurality of secondary devices, each of said secondary devices disposed between said first and second thermoplastic sheets and associated with one of said circuit paths.
 22. The sheet of heated element assemblies of claim 15, wherein at least one of said thermoplastic sheets includes a thermally conductive coating.
 23. A combination containment bag and heater with sidewalls, comprising: at least two heated element assemblies fused to each other along mating edges to form a containment bag with flexible sidewalls, each of said heated element assemblies comprising: (a) a first thermoplastic sheet; (b) a second thermoplastic sheet; and (c) a resistance heating element secured between and to said first and second thermoplastic sheets, said resistance heating element comprising: (i) a supporting substrate having a first surface thereon; (ii) an electrical resistance heating material joined to said supporting substrate, said electrical resistance heating material forming a predetermined circuit path having a pair of terminal end portions; and (iii) a pair of electrical connectors fixed to said terminal end portions of said electrical resistance heating material, said thermoplastic sheets and resistance heating element laminated together to form a continuous structure.
 24. The heated container of claim 23, further comprising a nozzle secured to said container, said nozzle providing access to an area defined within said container.
 25. A heated container, comprising: a heated element assembly, comprising: (a) a first thermoplastic sheet; (b) a second thermoplastic sheet; and (c) a resistance heating element secured between and to said first and second thermoplastic sheets, said resistance heating element comprising: (i) a supporting substrate having a first surface thereon; (ii) an electrical resistance heating material sewn to said supporting substrate with a thread, said electrical resistance heating material forming a predetermined circuit path having a pair of terminal end portions; (iii) a pair of electrical connectors fixed to said terminal end portions of said electrical resistance heating material; and (iv) a plurality of flap portions capable of rotation about a first axis of rotation, said circuit path continuing onto at least a portion of at least one of said flap portions, wherein said thermoplastic sheets and resistance heating element are laminated together to form a reformable continuous element structure, said continuous element structure formed into a final element assembly whereby said flap portions are rotated about said first axes to provide resistance heating in a plurality of planes.
 26. The heated container of claim 25, wherein said supporting substrate is shaped as a foldable profile of a container, said foldable profile including said plurality of flap portions.
 27. The heated container of claim 26, wherein said reformable continuous element structure substantially conforms to said foldable profile shape.
 28. The heated container of claim 27, wherein said continuous element structure includes at least one joining tab, said at least one joining tab mated to an adjacent surface of said continuous element structure in said final element assembly. 